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The different methods of extracting essential oils
There are three principal methods of extracting essential oils from aromatic plants. These are: expression processes; distillation processes; and extraction using volatile solvents.
This method is only used for citrus fruit. The essential oils in citrus fruits arc situated close to the surface of the peel and are easily obtained by squeezing and scarification (finely puncturing the peel). Expression methods include the sponge method and machine abrasion, the former being more traditional and producing a very pure essential oil.
You can experiment at home with hand expression and produce small quantities of your own citrus essential oils. Wash and dry the fruit and cut off segments of peel. Using your fingers, squeeze the peel over a small bowl to collect the drops of essential oil. Store them in a small, dark glass bottle with a dropper insert, and use them as you would any other citrus oil.
Distillation processes involve heating the plant material until a vapor is formed, then cooling the vapor until it becomes liquid. In water distillation, the plant material is covered in water and heated in a vacuum-sealed container. This method is slower and sometimes inferior to steam-distillation, because certain delicate components of essential oils are damaged by exposure to heat. The more efficient steam-distillation uses steam under pressure to swiftly extract the essential oil.
For the most delicate plant material, such as flowers, and for those containing only a small amount of essential oil, solvent extraction processes are used. The main advantage is that this method is gentle, but the resulting essential oils include non-volatile waxes and plant dyes, as well as the essential oil itself. Nonetheless, these essential oils are considered by many authorities to be fine for use in aromatherapy. The main solvents used in modern production are volatile hydrocarbons (such as hexane).
A recent innovation is a process called hypercritical carbon dioxide. This is reputed by some authorities to produce essential oils of very high quality and purity, though others are critical of oils produced in this way. The process requires very expensive equipment, so essential oils produced in this manner are difficult to obtain and expensive.